A bumper year for renewable generation capacity in 2017 has put the U.K. on course to meet its target for renewable-produced electricity. But the country still risks missing overall renewable energy targets because of sluggish progress on heat and transportation, a research firm has warned.

Last year saw renewable energy's share of electricity generation in the U.K. jump up by 4.8 percent, from 24.5 percent to 29.3 percent. This was the second-highest annual increase on record, after a 5.5 percent increase in 2015 that took the renewables share to 24.6 percent.

The 2017 boost puts the U.K. within spitting distance of its 30 percent target for renewable-based electricity generation by 2020. It will help the country meet its European Union (EU) and internal carbon budgets, said Tim Dixon, wholesale team leader at Cornwall Insight.

However, he added: “Unless greater progress is made for renewable heat and transport, where the U.K. is underperforming, then there remains a significant risk of us not meeting our 2020 renewable energy target, as well as our fourth and fifth carbon budgets.”

The U.K.’s carbon budgets are five-year caps on greenhouse gas emissions that were established in the wake of the country’s 2008 Climate Change Act. The Act commits the U.K. to cutting 2050 greenhouse gas emissions by at least 80 percent compared to 1990 levels.

The U.K. Department for Business, Energy & Industrial Strategy itself recognizes that. “In order to meet the fourth and fifth carbon budgets (covering the periods 2023 to 2027 and 2028 to 2032) we will need to drive a significant acceleration in the pace of decarbonization," it states.

The Department’s Clean Growth Strategy, published last year, envisages rolling out low-carbon heating and ending the sale of gasoline and diesel cars and vans by 2040. Up to 33 percent of a total GBP £2.5 billion ($3.2 billion) investment will be spent on transport, the Department for Business, Energy & Industrial Strategy says.

Nevertheless, according to Dixon, the most important step the U.K. could take for transport decarbonization would be to achieve cost parity of electric vehicles with internal combustion engine motors. This would likely not happen until the early 2020s, he said.

“Another important step will be the need for smart charging and how this impacts electricity networks,” he said.

For heat, meanwhile, the only schemes to date have been “less successful than for renewable electricity,” Dixon said.

Smart control and more efficient use of heat will need to be a priority for the country, he said, along with trials and studies into the potential of hydrogen and biogas for heating. The U.K. Clean Growth Strategy has allocated £250 million ($321 million) to "smart systems."

A government spokesperson told GTM that the country’s decarbonization plans would not be affected by the U.K.’s departure from the EU next year.

"We are seeking broad energy cooperation with the EU as part of our commitment to deliver cost-effective, clean and secure energy supplies,” the rep said, adding, "Leaving the EU will not affect the U.K.'s commitment to domestic and international efforts to tackle climate change, including the Paris Agreement."

Perversely, though, the U.K.’s rapid progress on renewables means Brexit could put the rest of Europe in danger of missing its renewable generation objectives.

The U.K. is already the world's biggest offshore wind player, with just over 7 gigawatts of capacity in operation and another 7 gigawatts under construction or secured in contracts.

And the government recently announced an expansion plan that could take the country's offshore wind capacity to 30 gigawatts. This dwarfs the offshore wind plans of European nations such as Germany, which is expected to install a little over 700 megawatts per year.

“While that's great news for the U.K.,” said Andrew Canning, press and communications manager at industry body WindEurope, “the EU will also stand to lose its most prominent offshore wind player.”

Losing the U.K. will have an impact on how EU countries divide up contributions to the block’s target of 32 percent renewable energy by 2030, he noted.

“With its ambitious offshore wind objectives, the U.K. could have taken more than its fair share of the EU's renewable target,” Canning said.